1. Field of the Invention
The present invention relates to the protection of hydrogen-containing hazards and the suppression of hydrogen combustion and fires.
2. Description of the Prior Art
The use of certain bromine-containing chemical agents for the extinguishment of fires is common. These agents are in general thought to be effective due to their interference with the normal chain reactions responsible for flame propagation. The most widely accepted mechanism for flame suppression is the radical trap mechanism proposed by Fryburg in "Review of Literature Pertinent to Fire Extinguishing Agents and to Basic Mechanisms Involved in Their Action", NACA-TN 2102 (1950). It is generally accepted that compounds containing the halogens chlorine, bromine and iodine act by interfering with free radical or ionic species in the flame; the presence of fluorine had not been considered as contributing to the fire extinguishing properties of a compound, but will impart stability, reduce toxicity and boiling point and increase thermal stability.
Various halogenated hydrocarbons have been employed as fire extinguishants. Prior to 1945, three halogenated extinguishing agents widely used were carbon tetrachloride, methyl bromide and bromochloromethane. For toxicological reasons, however, the use of these agents has been discontinued. The three fire extinguishing compounds presently in common use are bromine-containing compounds, Halon 1301 (CF.sub.3 Br), Halon 1211 (CF.sub.2 BrCl) and Halon 2402 (BrCF.sub.2 CF.sub.2 Br). The effectiveness of these three volatile bromine-containing compounds in extinguishing fires has been described in U.S. Pat. No. 4,014,799, issued to Owens. The National Fire Protection Association (NFPA) publication, The Fire Protection Handbook, Section 18, Chapter 2, entitled "Halogenated Agents and Systems" (1985) describes these agents in more detail.
Although the above-named bromine-containing compounds are effective fire fighting agents, those agents containing bromine or chlorine are asserted to be capable of the destruction of the earth's protective ozone layer. For example, Halon 1301 has an Ozone Depletion Potential (ODP) rating of 10, and Halon 1211 has an ODP of 3. As a result of concerns over ozone depletion, the production and sale of these agents after Jan. 1, 1994 is prohibited under international and United States policy.
It is therefore an object of this invention to provide a method for extinguishing fires as rapidly and effectively as the techniques using presently employed Halons while avoiding the above-named drawbacks.
Hydrogen is an important industrial chemical in petroleum refining, in the synthesis of methanol and ammonia, and in the manufacture of various chemicals. Hydrogen also finds use in metallurgical processing, vegetable-oil hydrogenation, electronics manufacture and fuel cell applications (Kirk-Othmer Encyclopedia of Chemical Technology, 5th ed., volume 13). The danger in the use of hydrogen lies in its extreme flammability in oxygen or air. Hydrogen is odorless, colorless, and burns with an almost invisible flame. As a result, hydrogen is not readily detected, further increasing the danger of its use compared to other flammable substances. Detonation and flammability limits for hydrogen are wider than those of most other flammable gases.
The difficulty of suppressing hydrogen combustion and fires is evident from the large quantities of Halons, in particular Halon 1301, required for suppression. Whereas a large selection of Class A and Class B fuels are sufficiently protected by a concentration of 5 percent by volume Halon 1301, suppression of hydrogen fires with Halon 1301 requires at least 20 percent by volume Halon 1301 (C. E. Ford, Halon 1301 Fire-Extinguishing Agent: Properties and Applications, in Fire Protection by Halons, NFPA, 1975.).
It is a further object of this invention to provide an agent for use in a method for the suppression of hydrogen combustion that is efficient, economical and environmentally safe with regard to ozone depletion.
The use of certain bromine-containing chemical agents such as Halon 1301 to provide an inert atmosphere which is incapable of supporting combustion is also known, and such applications are commonly referred to as inerting applications, as opposed to extinguishing applications. In inerting applications an enclosure containing a combustible hazard is filled with sufficient quantities of the inerting agent such that the resulting atmosphere will not support combustion of the otherwise combustible hazard. Hence, even in the case that an ignition source is activated, for example an electric arc or electrostatic spark, combustion does not occur. Inerting applications include explosion suppression and the protection of areas containing combustible and/or flammable materials.
The difficulty of suppressing hydrogen combustion is evident from the large quantities of Halons required for the inertion of hydrogen/air mixtures. Whereas the inertion of a large selection of fuels requires Halon 1211 or Halon 1301 concentrations in the range of 4 to 10 percent by volume, the inertion of hydrogen/air mixtures requires concentrations in excess of 20 percent by volume Halon 1211 or Halon 1301 (C. L. Ford, in Halogenated Fire Suppressants, ACS Symposium Series 16, ACS, 1975.)
It is a further object of this invention to provide an atmosphere which does not support the combustion of hydrogen that is efficient, economical and environmentally safe with regard to ozone depletion.